Advanced continuous warhead

ABSTRACT

An improved continuous rod warhead mechanism featuring increased rod ejection velocity is disclosed. The more efficient warhead of the present invention is characterized by multipoint axial initiation and by a plurality of pressed grain explosives of desired detonation rates for producing a cylindrically expanding detonation wave front for meeting the rods face-on. Normal incidence of the detonation front on the rods may be employed without destroying ring continuity, thereby resulting in more efficient energy transfer and higher rod velocity.

6 United States Patent 1 [111 3,742,856

Welanetz July 3, 1973 [54] ADVANCED CONTINUOUS WARHEAD 3,490,374 l/l970 Nooker 102/67 3,4 4 31970 C d 102 [75] Inventor: Ludolph F. Welanetz, Rockvtlle, Md. 98 22 I or at 81 I67 [73] Assignee: The United States of America as Primary Examiner-Verlin R. Pendegrass represented by the Secretary of the Attorney-R. S. Sciascia, J. A. Cooke and R. J. Navy, Washington, DC. Ericksen [22] Filed: June 30, 1969 [21 Appl. No.: 839,795 ABSTRACT An improved continuous rod warhead mechanism fea 7 turing increased rod ejection velocity is disclosed. The [52] US. Cl. 102/67 more efficiem warhead of the present invention is Chap [51] Int. Cl. F42b 13/48 acterized by multlpomt axial initiation and by a plural- [58] Field of Search 102/67, 70, 70.2 I,

ity of pressed grain explosives of desired detonation 102/24 HC, 24, 28 EB rates for producing a cylindrlcally expandlng detona- 56] Reierences cited tion wave front for meeting the rods face-on. Normal incidence of the detonation front on the rods may be UNITED STATES PATENTS employed without destroying ring continuity, thereby 3,145,656 8/l964 Cook et al 102/24 HC resulting in more efficient energy transfer and higher 3,170,402 2/1965 Morton et al 102/70 rod velocity 3,245,353 4/1966 Gilbertson et aL... 3,264,990 8/1966 Betts 102/28 EB 9 Claims, 3 Drawing Figures PATENTEBJULB I975 F'IG.2

INVENTOR LUDOLPH E WELANETZ ATT NEY FIG.3

ADVANCED CONTINUOUS WARI-IEAD BACKGROUND AND SUMMARY OF THE INVENTION warheads utilizing a continuous rod projectile mechanism have been demonstrated to provide a most effective damaging agent, particularly in an aerial environment. Since continuous rod warheads are relatively recent innovations, the configurations presently in use will be subject to extensive and perhaps radical improvement over a period of time. The present invention envisions an improvement particularly directed to enhancement of the near term effectiveness of a continuous rod warhead. Generally, the present invention is directed to increasing the ejection velocity of the continuous rod ring without degradation of the components of the ring. To this end, a number of inventive al terations are proposed which exhibit compatibility with present technical and economic production modes.

Present day continuous rod warheads generally comprise a cylindrical body of an explosive material detonated at the center of one end. A rod mat concentric to the explosive body is usually double-layered with rod ends of the inner layer being suitably welded to rod ends of the outer layer to form a continuous chain. The explosive body is encased within an inner skin and is confined at its ends by suitable plates. The rod mat is supported between the inner and an outer skin, the skins being usually fastened to end rings associated with the aforementioned confining plates. Detonation of the warhead is most often accomplished through use of a booster charge from an explosive train which contains primary explosive and is interrupted by an arming device. The warhead is supported at its ends by structural components of the missile air frame. In operation the rods must pass through the missile skin and other associated obstructions, thus reducing the rod velocity. If rod breakup occurs, warhead effectiveness is materially reduced.

The present invention envisions a plurality of inventive alterations which taken singly or in combination serve to enhance warhead effectiveness by increasing the rod ejection velocity. Previous attempts directed to improving continuous rod warhead performance by increased rod velocity have met with failure to prevent spalling or mashing of the rods. In work leading to the present invention, a number of useful approaches to the problem have been found. In the first instance, acceleration of rods to a high velocity can be accomplished without spalling or mashing if proper confinement of the explosive charge is provided. Secondly, normal incidence of the detonation front on the rods may be employed without damage to the rods. Additionally, a buffer layer between the rods and the explosive is not required, given ajudicious choice of rod material, explosive composition, and warhead construction.

Specific features incorporated in the present warhead include multipoint axial initiation and the use of a plurality of different explosives for wave shaping. Simultaneous initiation of detonation sites is now feasible and has been described in the warhead art. The present invention illustrates the application of this concept to a continuous rod explosive device without injury to the individual rods or to the resultant ring geometry. Similarly detonation wave shaping through the use of a number of different explosives is also an established technique in the warhead art. Patents relative to the concurrent use of oxidizable high energy materials in solid fuel rockets have been issued to Fox, U.S. Pat. No. 3,144,829, and to Keathley et al., U.S. Pat. No. 3,008,417. Presently attainable uniformity in explosive's forming allows the use of the shaped explosive combinations necessary to the operation of the high performance warhead of the present invention.

, By way of summary, the present invention envisions a high performance continuous rod warhead having improved performance due in large measure to increased rod ejection velocity. This velocity increase is obtained by the present warhead which provides the following features:

1. a cylindrically expanding detonation front'meeting the warhead rods face-on;

2. a multipoint axial initiator utilizing the exploding bridgewire principle of the initiation using only secondary explosive;

3. the use of two or more explosive compositions for detonation wave shaping, the explosive grains being assembled from pressed compositions of dense, high energy explosive of desired detonation rates;

4. a single layer of rods each having a rectangular cross-section and being composed of straight carbon or low alloy steel;

5. a lightweight casing for the explosive; and

6. a primary structural support enclosed within the explosive.

It is therefore a primary object of the invention to provide an improved continuous rod explosive device characterized by increased rod ejection velocity.

It is also an object of the invention to provide an explosive combination of materials in a continuous rod warhead for producing an efficient cylindrically expanding detonation wave front.

It is a further object of the invention to provide a continuous rod explosive device of improved effectiveness wherein increased ring velocity is attained without mashing or spalling of the individual rods.

Further objects and advantages of the invention are to be seen in the following description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-section taken perpendicular to the axis of the warhead;

FIG. 2 is an axial section on the line 2-2 of FIG. 1; and

FIG. 3 is a chart representing the cross-section of the warhead in the region of a point of initiation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Short term performance improvement for continuous rod warheads is best obtainable by increasing the ejection velocity of the continuous rod ring. Previously, the feasibility of such an approach was subject to question, since attempts to increase rod ejection velocity resulted in spalled rods and premature ring break-up. By utilizing the design characteristics to be detailed hereinafter, a more effective continuous rod warhead is obtained.

In order to achieve increased warhead performance, a cylindrically expanding detonation wave initiated along the warhead axis is desired. This detonation wave impinges on the warhead casing without obliquity and of detonation wave has been avoided because of the high shock pressures induced in the casing material,

causing undesirable metal break-up and spalling. However, through proper confinement of the explosive charge, more efficient transfer of energy from. the explosive to the casing and thus to the rods is obtained.

Detonation wave shaping is brought about through the concomitant use of the several features of the invention. As a first example, multipoint axial initiation of the explosive warhead is an essential to the formation of a face-on wave which will impart increased velocity to the rods rather than destroy them. Systems suitable for effecting this type of initiation are now available and are known as exploding bridgewire initiators. In this initiation system, a high energy pulse of electricity is impressed upon a fine wire causing it to explode, thereby forming an expanding plasma and causing both a strong shock wave and high temperature wave to be transmitted into a surrounding explosive material. The transmitted energy level is of sufficient magnitude to initiate detonation in a relatively insensitive secondary explosive. Such a device is inherently more reliable and safer than conventional electroexplosive devices and may therefore be permanently placed in a warhead without an intervening safety and arming mechanism. Although a large source of electrical energy is required, recent advances in compact power supply systems minimize this possible disadvantage.

The number of points of initiation required for effective wave shaping depends primarily on a second feature of the invention, that is, the use of two or more distinct geometrical regions of explosive material having differing detonation velocities. As will be described more fully hereinafter, an explosive material having a first detonation velocity is formed into a preferred geometry. A second explosive material having a second detonation velocity unequal to the first detonation velocity is formed into a complementary geometry. The volumes of explosives thus formed are subsequently joined into a complete explosive assembly, the assembly having a combination of explosive material with differing detonation velocities. By proper choice of explosive geometry and detonation velocities, a desired detonation wave front is produced.

A few design principles of continuous rod warheads are commonly accepted. One is that the warhead itself should not be used as a structural member to transfer loads between the missile structure forward and aft of the warhead. This function is normally performed by the missile skin surrounding the warhead compartment, thus resulting in a loss of kinetic energy as the rods pass through the skin in their outward travel. In order to increase warhead support, the present invention contemplates use of a principal structural member enclosed within the main body of explosive material and which is fastened to end plates fore and aft of the main explosive body. The enclosed structural member has a preferred star-shaped section to be described in more detail hereinafter. With the warhead thus supported, a more lightweight skin material may be used.

A second structural consideration is that the warhead should be supported only at its ends. Any material around the surface of the main explosive body in addition to the usual rod mat must be accelerated with the rods. The resulting kinetic energy absorbed by this material does not produce useful target damage and thereby reduces warhead effectiveness. Simple endsupported beam construction should thus be employed for suspension of the warhead.

Thirdly, the rod mat itself should not comprise a portion of the warhead primary structure. At best, the rods should not even support themselves. In order for proper outward projection of the rod mat to occur, any constraint offered by end attachments to the rods must be eliminated, hereby preventing the introduction of forces which will adversely affect rod motion.

A further structural consideration is the preferred enclosure of the main body of explosive material within a container having a smoothly contoured inner surface coated with a layer of suitable non-metallic material. Since the explosive should not be required to contribute to the structural support of the warhead, the container must provide this additional support. The container may also serve as part of the support for the rod mat. A suitable material for the container is sheet steel.

The primary features of the present warhead may thus be summarized as follows:

1. detonation wave shaping to form a cylindrically expanding detonation front for meeting the rods faceon, thereby increasing rod ejection velocity;

2. multipoint axial initiation and the use of two or more explosive compositions having differing detonation velocities for effecting the aforementioned wave shaping;

3. initiation by the exploding bridgewire principle using only secondary explosives;

4. a single layer of rods of generally rectangular cross-section and of straight carbon steel or low alloy steel;

Sfuse of a lightweight'casing for the explosive and for the rods; and

6. a primary structural support within the explosive and which preferably has a star-shaped crosssection.

Considering the above-described design features, the following description of a preferred embodiment of the invention is given and is referenced to the drawings wherein the warhead is shown generally at l in FIGS.

.1 and 2. Referring to the FIGS. 1 and 2, the warhead 1 is seen to be generally cylindrical in shape, having an external structure comprising forward and aft end plates 3 and 5 respectively and a lightweight external skin 7. The end plates 3 and 5 serve to confine the explosive material disposed within the warhead and also are structurally joined to an internal supporting structure interior of the warhead which will hereinafter be described. Further, the end plates 3 and 5 are joined to the airframe of a missile (not shown), thereby providing the only points of support offered by the missile structure. Various methods of effecting this juncture existing in the art and therefore need not be described.

The external skin 7 is comprised of any suitable lightweight material, the principal object of the skin being to provide support evenly along the outer surface of a rod mat 9. The rod mat 9, which may comprise a single layer of rectangular rods and with a radial dimension roughly twice the circumferential dimension, is further supported on its inner surface by a lightweight internal skin 11. The invention also envisions the use of doublelayered or treble-layered rod mats, the use of which depends primarily on the particular mission of the warhead. The particular structure of the rod mat and the particular procedures used for joining the individual rods within the mat are not considered to be within the scope of the invention since suitable mat structures and welding techniques are known in the prior art.

The internal skin 11 further serves to enclose an explosive assembly 13, which is a combination of geometrically arranged explosive compositions A, B, and C. The skin 11 provides a container for the explosive assembly 13, the inner surface 12 of said skin contacting said assembly 13 being of a smooth contour and being preferably coated with a layer of suitable non-metallic material such as Teflon. For simplicity, the nonmetallic layer is not shown in the Figure.

As noted, the explosive assembly 13 comprises the combination of explosive compositions A, B, and C. The explosive compositions A, B, and C have differing detonation velocities which produce, concomitant with the particular geometries of the compositions, a cylindrically expanding detonation wave front which meets the rod mat 9 face-on. A more detailed description of the means and method employed in shaping the detonation wave front is given hereinafter.

As can be particularly seen in FIG. 2, the explosive composition A is formed into radial wedges 15 which taper to apices 17. The wedges 15 are disposed regularly and evenly along the axis of the warhead l and are embedded in the explosive composition B. The explosive composition B effectively forms wedges 19 which are complementary to the radial wedges 15 of the explosive A and which taper to apices 20. The wedges l9 fit into the spaces between the radial wedges 15, the sides of the wedges 19 fitting flush along the sides of the wedges 15. The two explosive compositions are preferably cemented together with a thin, uniform layer of suitable adhesive. Those portions 21 and 23 of the explosive composition A not directly opposite the rod mat 9 need not be formed as specified above, but may simply form cylindrical end masses of explosive. The portions 21 and 23 extend well beyond each end of the rod mat 9 in order to afford effective confinement to the gaseous products of the detonation process so that the rod components of the rod mat 9 may be uniformly accelerated. Explosive C is seen to form a cylindrical sleeve 25 contiguous to and surrounding the explosive compositions A and B. Although proper wave shaping may be effected without the use of the explosive sleeve 25, that is, with only the two explosive compositions A and B; the explosive sleeve 25 is conveniently utilized to provide additional energy to the cylindrically expanding wave front produced by the explosive compositions A and B. Thus, the explosive C is chosen for high energy content or low brisance.

Explosive A, as will be further described hereinafter, is formed of an explosive material having a high detonation velocity relative to the detonation velocity of explosive B. For example, the explosive A may be an explosive material known as Composition B and the explosive B may be trinitrotoluene. Proper choice of explosive material is also governed by the need for high energy and high density explosive grains of uniform density and homogeneity which also exhibit chemical stability, dimensional stability, and resistance to heat. Explosive materials having these properties are presently available. It may be further stated here that pressing of the explosive compositions A, B and C into the required geometries is preferred due to the degree of control afforded by the pressing process over the homogeneity, density, and dimensions of the explosives.

Detonation initiation of the explosive assembly 13 is afforded by an exploding bridgewire assembly 27 disposed within a housing 31 along the axis of the warhead 1. The bridgewire assembly 27 is contained within a cylindrical housing 29 which is insertable into the housing 31. The cylindrical housing 29 is constructed of an electrically conductive material for purposes to be described hereinafter. The bridgewire assembly 27 comprises relatively fine wire segments 35 and relatively large or coarse wire segments 33 which are alternately disposed along the axis of the warhead 1 and which are welded end to end to form an electrically conductive path. The segments 35 and 33 are further embedded in a relatively insensitive explosive material 37 such as is commonly used with detonation initiators of this type. At the forward end of the warhead 1, that is, the end confined by the end plate 3, one of the relatively large wire segments 33 terminates the joined wire segments and is connected to an electrically conductive plate 39 which is welded to the cylindrical housing 29. At the other end of the warhead 1, that is, the end confined by the end plate 5, one of the relatively large wire segments 33 terminates the joined wire segments and extends through the end plate 5 and is attached to a high energy compact power supply (not shown) which may be conveniently disposed in any portion of the missile, however remote from the warhead itself. According to the invention, the fine wire segments 35 are disposed opposite the apices 20, of explosive composition B. Detonation of the explosive assembly 13 is effected by impressing a high energy pulse of electrical energy upon the alternately joined wire segments 33 and 35,

thereby causing the fine wire segments 35 to explode.

The heat and shock from the expanding plasma produced on explosion of the wire segments 35 causes detonation of the relatively insensitive explosive 37. The strong shock wave and elevated temperature thus produced are sufi'lcient to detonate the warhead itself. Thus axial, multipoint initiation of the warhead may preferably be effected, although it is to be understood that other detonation initiation schemes providing axial multipoint initiation may be used with the present warhead. With the assembly 27 described, the detonation initiation system may be maintained in place at all times without the need for an intervening safety and arming device. The weight penalty caused by the need for an electrical power supply is more than offset by the advantages of the bridgewire assembly 27. The detonating system may utilize exploding bridgewires in series, as shown, and wherein the return electrical path is provided by the electrically conductive cylindrical housing 29, or in parallel, depending on the characteristics of the power supply being used.

As can be seen in FIGS. 1 and 2, warhead structural support is provided by a plurality of spaced, radially directed, hollow beams 41 longitudinally disposed internal of the explosive assembly 13. The beams 41 extend throughout the entire length of the explosive assembly 13 and are attached to the end plates 3 and 5. The beams 41 provide structural support for the warhead, preventing the imposition of supporting loading on the explosive assembly 13. Electrical cables 43 which normally extend through the warhead compartment of a missile may be disposed within the hollow beams 41 without hindering the explosive portion of the warhead.

As has been previously stated, the explosive assembly U is designed to produce a uniform, cylindrically expanding detonation wave front for meeting the rod mat 9 face-on, thereby increasing the ejection velocity of the resultant continuous rod ring to produce an improved high performance continuous rod warhead. A quantitative description of the rnultipoint axial initiation and geometrical assemblage of explosive material having differing detonation velocities is appropriate here. The principle of operation may be understood by assuming the explosive assembly 13 to be a single homogeneous explosive material. Axial, multipoint initiation of this single material as provided hereinabove would produce a series of spherically expanding detonation wave fronts, one emanating from each point of initiation. These detonation fronts would intersect resulting in a highly non-uniform surface. By introducing an explosive having a slightly lower detonation velocity into the region of the transverse plane containing each point of initiation, that is, explosive B disposed as the wedges 19, the detonation front in this region is slightly retarded with the effect of making the front be more nearly cylindrical.

The smoothness of the detonation front may be calculated with reference to FIG. 3, the Figure representing the axial cross-section of the warhead in the region of a point in initiation 45. The point 45 is taken to be located at the origin of the axes x and y. Let A represent the region of explosive material having higher detonation velocity D and B the'region of explosive material having lower detonation velocity D,,. On detonation initiation at the point 45, the time for the detonation front to proceed from the point 45 to the apex of explosive A may be obtained from:

A convenient form of Equation (2) is While the detonation front in explosive B has advanced, as described above, the front in explosive A has expanded such that, at the interface between the two explosives, the radial location of the front y may be calculated to be:

ya yr dn cos 4n w/ r5 yr dn where r D t.

Equation (4) may be reduced to:

The amount of non-uniformity of the detonation front may be measured by the quantity (y, y,;). This quantity may be calculated from:

Eq. 7 As an example of the degree of smoothness achievable, it may be assumed that b, 30 and D /D cos (1),.

The following table, calculated with the aid of Equation 7 gives values of the smoothness criterion for corresponding values of t/t,:

t/t l 2 3 4 YA .YB/y 0 0.062 0.080 0.087

It is seen that by proper choice of the ratio of the detonation velocities of the two explosives, the smoothness of the front can be improved at any desired radius thereof.

With regard to the provision of the explosive composition C as the sleeve 25 surrounding the explosive compositions A and B, the explosive composition C may be chosen to have a detonation velocity equal to either of the detonation velocities of the explosive compositions A or B or said composition C may have a detonation velocity different from either. Since spherically expanding detonation fronts intersect in the explosive composition B, originating from adjacent points if initiation, the meeting waves thus produced may be controlled at the juncture of the explosive compositions A and B with explosive composition C by the simple incorporation of an annular void or buffer region at the juncture for dissipating the meeting waves. Such provision of an annular void does not form a part of the preferred embodiment of the invention but, as in a number of existing continuous rod .warhead devices, may be provided as being within the scope of the invention as recited in the appended claims.

I claim:

1. An improved high performance continuous rod warhead having a rod mat, the warhead comprising:

explosive means disposed within the warhead and having an axis therethrough, said means comprising separate and distinct regions of high energy explosive materials having unequal detonation velocities,

a first region of said explosive means comprising a first explosive material having a plurality of circular wedges radially extending from the axis substantially normal thereto, and

a second region of said explosive means comprising a second explosive material lying between and contiguous to said plurality of circular wedges of the first explosive material, the second explosive material effectively forming complementary wedge-like masses disposed flush with and contiguous to the first explosive material in the first region; and

detonation means axially disposed within the exposive means for inititating detonation at a multiplicity of points evenly spaced along the axis of said explosive means,

detonation .of the warhead producing a cylindrically expanding detonation wave front for causing a more efficient energy transfer from the explosive means to the rod mat, thereby resulting in increased ejection velocity of the rods of the rod mat.

2. The continuous rod warhead of claim 1 wherein said first explosive composition has a relatively higher detonation velocity than that of the second explosive composition.

3. The continuous rod warhead of claim 1 wherein the rod mat is disposed parallel to the axis of the explosive assembly and in proximous disposition to the assembly and wherein the inter-related wedge-like regions of the first and second explosive compositions extend beyond the ends of the rod rnat, whereupon the cylindrically expanding detonation wave front produced on detonation of the warhead will impinge on the rod mat without obliquity.

4. The continuous rod warhead of claim 1, and further comprising a cylindrical sleeve of a third explosive material contiguous to and surrounding the explosive assembly which is comprised of the first and second explosive compositions.

5. The explosive continuous rod warhead of claim 1 wherein the explosive means comprises an explosive combination of high energy materials pressed into a cylindrical configuration.

6. The continuous rod warhead of claim 1 and further comprising internal structural support means, said support means comprising a plurality of beams disposed within the explosive means, extending longitudinally throughout said explosive means, and being joined to respective ends of the warhead.

7. The continuous rod warhead of claim 6 and further comprising cables extending through the beams, and through the warhead.

8. The continuous rod warhead of claim 1 wherein said detonation means comprises an exploding bridgewire initiation system for effecting axial, multipoint detonation of the explosive means.

9. The continuous rod warhead of claim 1 and further 7 comprising an internal skin for enclosing and supporting the explosive means, the skin having a smoothly eontoured inner surface; and,

an outer skin wherein the rod mat is disposed with its 

1. An improved high performance continuous rod warhead having a rod mat, the warhead comprising: explosive means disposed within the warhead and having an axis therethrough, said means comprising separate and distinct regions of high energy explosive materials having unequal detonation velocities, a first region of said explosive means comprising a first explosive material having a plurality of circular wedges radially extending from the axis substantially normal thereto, and a second region of said explosive means comprising a second explosive material lying between and contiguous to said plurality of circular wedges of the first explosive material, the second explosive material effectively forming complementary wedge-like masses disposed flush with and contiguous to the first explosive material in the first region; and detonation means axially disposed within the exposive means for inititating detonation at a multiplicity of points evenly spaced along the axis of said explosive means, detonation of the warhead producing a cylindrically expanding detonation wave front for causing a more efficient energy transfer from the explosive means to the rod mat, thereby resulting in increased ejection velocity of the rods of the rod mat.
 2. The continuous rod warhead of claim 1 wherein said first explosive composition has a relatively hiGher detonation velocity than that of the second explosive composition.
 3. The continuous rod warhead of claim 1 wherein the rod mat is disposed parallel to the axis of the explosive assembly and in proximous disposition to the assembly and wherein the inter-related wedge-like regions of the first and second explosive compositions extend beyond the ends of the rod mat, whereupon the cylindrically expanding detonation wave front produced on detonation of the warhead will impinge on the rod mat without obliquity.
 4. The continuous rod warhead of claim 1, and further comprising a cylindrical sleeve of a third explosive material contiguous to and surrounding the explosive assembly which is comprised of the first and second explosive compositions.
 5. The explosive continuous rod warhead of claim 1 wherein the explosive means comprises an explosive combination of high energy materials pressed into a cylindrical configuration.
 6. The continuous rod warhead of claim 1 and further comprising internal structural support means, said support means comprising a plurality of beams disposed within the explosive means, extending longitudinally throughout said explosive means, and being joined to respective ends of the warhead.
 7. The continuous rod warhead of claim 6 and further comprising cables extending through the beams, and through the warhead.
 8. The continuous rod warhead of claim 1 wherein said detonation means comprises an exploding bridgewire initiation system for effecting axial, multipoint detonation of the explosive means.
 9. The continuous rod warhead of claim 1 and further comprising an internal skin for enclosing and supporting the explosive means, the skin having a smoothly contoured inner surface; and, an outer skin wherein the rod mat is disposed with its inner surface contiguous to the outer surface of the internal skin and with its outer surface contiguous to the inner surface of the outer skin, whereby the rod mat is constrained between the said skins, the ends of the rod mat being free of any structural restraint. 